Level and source of 129I of environmental samples in Xi'an region, China

Iodine-129 is widely used as a tracer in various environmental practices such as monitoring of nuclear environmental safety, seawater exchange and transport, geochemical cycle of stable iodine and dating of geological events. The spatial distribution of 129I concentration varies significantly on global scale because of anthropogenic input from nuclear activities coupled with scarcity of data on environmental 129I variability in many parts of the world including Asia. Here we report new data on 129I and 127I concentrations in soil, vegetation, river water and precipitation collected from Xi'an area, China. The results indicate values for environmental 129I/127I ratios in the investigated area range from 1.1 × 10− 10 to 43.5 × 10− 10 with a mean of 20.6 × 10− 10, which is 1–3 orders of magnitude lower than the ratios observed in Europe, but comparable with those observed in the locations far from direct effect of point release sources and at similar latitude. The main source of 129I in the investigated area is attributed to the global fallout of both atmospheric nuclear weapons testing and long distance dispersion of fuel reprocessing releases.

Research highlights
► We present the first investigation of anthropogenic radioactive 129I in the terrestrial environment in middle China.
► River water, surface soil and vegetation samples from Xi'an region were analyzed for 129I and stable 127I.
► The distribution, source term, and transfer from soil to plants of 129I in middle China are presented.
► AMS shows its unique capacity in 129I analysis and environmental safety research using 129I and other radionuclides.
► The results supplied a basic data for evaluating nuclear risk in the future.